The traditional eyeglass frame consisting of a front rim, or central element, for fastening and supporting the lenses and whose ends are furnished with hinge elements for fastening and moving the temples, has been substantially revolutionized by the introduction of eyeglasses known as “ultralight” or “three-piece” eyeglasses where the lenses are joined directly to each other and to the temples solely by an interposed central bridge and a pair of lateral fastening hinge elements.
According to the prior art, the main feature of the method for forming a pair of “ultralight” eyeglasses is that of providing the ends of the central bridge and one of the two ends of the two lateral hinge elements connecting the eyeglass temples with a special fork-like structure at right angles to the plane of the lenses, the two prongs of each fork being designed to be inserted into corresponding pairs of holes made near the central and lateral edges of one lens.
All the prior art solutions of “ultralight” eyeglasses have had to overcome, for eyeglass solidity and durability, at least two structural problems connected with the firmness of the join between the edge of the lens and the central bridge element and with lens rattling relative to its fastening points.
More specifically, to eliminate rattling at the lens fastening points, most prior art solutions contemplate the presence, on each side of the lens edge, of a pair of through holes, or one through hole associated with one or more blind holes, or even with a lateral open hole, in which there is a fastener acting in conjunction with the retaining wire to prevent any form of lens rattling.
One prior art system for fastening the lenses to the mounting structure of ultralight eyeglasses is described in WO 03/083553. According to the system described in that document, the ends of the structural parts of the eyeglasses, namely, the central bridge and the lateral hinge elements, are furnished with two pairs of cylindrical pins made of amorphous plastic material, with annular enlargements, while a corresponding pair of holes in the lens is provided with and covered by a pair of sleeves which are joined to each other by a stop plate and to which are made of crystalline plastic material, to house in their cavities the cylindrical pins of the structural parts of the eyeglasses, in such a way that the annular enlargements of the pins push the outside surface of the respective sleeves to solidly engage the lateral surface of the lens holes, thus fixedly joining the lenses to the central bridge and to the lateral hinge elements of the eyeglass temples.
That solution, in turn derived from a similar lens fastening system proposed by patent EP 0561763 of Mar. 12, 1993, substantially meets the need to join the lenses of ultralight eyeglasses without using fastening screws to join the lenses to the other eyeglass parts, and thereby overcoming the frequent problem of lens cracking.
Use of that solution, however, has revealed a first drawback in the fact that the pins made of plastic material, besides having low mechanical strength—for example, low shock resistance—must nevertheless be made and specifically fixed to, or incorporated in, the ends of the bridges and of the lateral hinge elements, since they are made of different materials at different times and in different moulds from the parts they must be joined to, thus influencing the working times and conditions, as well as the costs of the eyeglasses.
Another drawback of that solution is due to the fact that, in the case of lenses which are thicker than average, the uniform and limited height of the fastening pins provides a relatively insecure fastening because the relative penetration of the pins into the lenses makes the free ends of the securing sleeves excessively flexible.
A yet further drawback of the stated prior art system is due to the impossibility of applying the fastening pins to the bridges and hinge elements made, for example, by die forming or punching out of metal sheets not only because of the relatively reduced thickness of their structure but also because of the impossibility of solidly joining them to those parts of the eyeglasses. This drawback has become more critical with the increase in the use of this method for the forming of high-quality sheeting made, for example, from titanium alloys for the manufacture of hinge elements, temples and even fronts for eyeglasses of all kinds and designs.
Another prior art example of a method for fastening the bridge and temples to the lenses without using threaded parts is described in US 2005/034287. As described in that document, the bridge and the hinge elements connecting the temples to the lenses are punched out from a thin metal plate. At the ends of them, they are provided with protruding members, each having ratchet-like teeth whose side walls are furnished with downwardly inclined barb-like projections. When fitting the lenses, the ratchet-like teeth are inserted directly into matching holes made in the lenses and the ends of them are left to protrude from the outside surface of the lenses.
The protruding ends are covered by a capping piece with hollowed-out holes into which they are inserted.
This further system of making ultralight eyeglasses without using threaded parts, although it allows the use of connecting elements punched out from thin metal sheeting, nevertheless has the disadvantage of having to insert the barbed, ratchet-like teeth into the holes in the lenses, with a high risk of damaging and cracking the lenses.
Moreover, forming the barbed surfaces on the side walls of the ratchet-like teeth requires the use of complex shaped dies which are expensive and quick to deteriorate.
A system for producing ultralight eyeglasses whose lens mounting structure consists of a bridge and two lateral hinge elements or end pieces made by punching out from quality sheeting is described in Italian patent application IT-BL2004A000011 dated Apr. 29, 2004.
In the system described in that application, each end of the lens mounting structure is furnished with a pair of teeth. The eye of a lens retaining wire is positioned between the teeth. The wire is fed through a hole made in the lens, while the teeth are inserted into corresponding sockets made in the lens radially relative to the holes through which the retaining wire is fed, thus holding the lens firmly in place when the retaining wire is fastened by a suitable lock nut.
The practical application of this solution has, in effect, allowed use of the new and advantageous technique of making bridges and end pieces by die forming from sheets made of quality material but has not entirely eliminated the problems of cracking caused by excessive tension applied by the retaining wire on the lens or the problems of looseness resulting from insufficient tightness of the retaining wire.
Patent document US 2005/275793 discloses eyeglasses where the temples and bridge are fixed to the lenses by means of pin-like teeth with rectangular cross section which are pressed into notches formed inside holes made in the lenses.
To anchor the teeth in the respective notches, the tooth surfaces have saw-tooth indentations on them.
The disadvantage of this solution is that the relative difficulty of engaging the teeth in the respective notches is not compensated by a particularly effective and secure hold of the bridge and temples on the lenses.
Thus, that system for fastening the bridge and temples is relatively unreliable and insecure.